Element for photocells and rectifiers



Aug. 18, 1942. I c. e. FlNK EI'AL ELEMENT FOR PHOTOCELLS AND RECTIFIERS Original Filed Aug. 10} 1%40 /2 /4 I \f I 2//Z mvzszvroxs COL IN qF/NK B EDWARD A01. [/2

a ATTORNEY Patented Aug. 18, 1942 ELEMENT Fon rno'rooELLs AND RECTIFIERS Colin Garfield Fink and Edward Adler, New York, N. Y.

Continuation of application Serial No. 352,134, August 10, 1940. i This application June 10. 1941, Serial No. 397,404

12 Claims. (Cl. 175-366) This invention relates to elements for photocells and rectifiers having light sensitivity and asymmetrical conducting electrical properties, and to the method of manufacture thereof; and provides improvements therein. i

Elements of the solid, cuprous oxide, type, fo photocells and rectifiers have heretofore been used.

It has also heretofore been proposed to increase the light sensitivity of such elements. For example, according to Fink and Fogle, Transactions of the Electrochemical Society, vol. 66, page 305, the photo-activity of such elements may be increased by subjecting' the surface of the cuprous oxide to an acid etc-h, using solutions of nitric acid, hydrochloric acid, etc. Another method is to sensitize the surface of the cuprous oxide by ionic bombardment in a glow-discharge.

Cuprous oxide elements sensitized by previously known methods deteriorate or age rather quickly. Muller and Teeters, Trans. Electro chemical Society, vol 69, page 467, reported that, after fiif teen minutes, following sensitization by sputtering in a glow-discharge, the output of a,

cuprous oxide photocell dropped from an initial value of 570 mieroampercs to 2'75 microamperes. The ageing, accompanied by decrease in photoactivity continued throughout the life of the cell, although more slowly after the sharp initial drop in activity. Muller and Teeters attributed the deterioration to a reaction between one of the atmospheric constituents, such as oxygen, or carbon dioxide, and the sensitized surface at the interface between the cuprous oxide and the front electrode.

Similarly the elements, when used for rectifying alternating current, do not have the desired stability, and age, or lose efficiency in a relatively short time.

The present invention provides a new and improved method of increasing the sensitivity or output of a photoelectric element of the cuprous oxide type." The invention further provides an element of the type described having an improved output or sensitivity, improved electrical conductivity at the junction between the cuprous oxide layer and the front electrode, and improved stability and resistance to deterioration due to handling, ageing, ordinary use, or to harmful interaction with certain atmospheric constituents.

The invention further provides a rectifier element of the type described having an improved electrical conductivity and electrical contact at the junction between the cuprous oxide layer iii and the front electrode, and improved stability and resistance to deterioration due to handling, ageing, ordinary use, or to harmful interaction with certain atmospheric constituents.

The invention further provides an element of the type described in which the leakage of current, when the element is used for rectification, in the reverse or high resistance direction is reduced.

Embodiments of the invention are illustrated in the accompanying drawing, wherein:

Fig. 1.-is a diagrammatic cross-section, of an element according to the present invention, with adaptations for use as part of a photo-electric cell. 1

Fig. 2 is a view similar to Fig. 1 illustrating the element with adaptations for use in an apparatus for rectifying alternating current.

The present invention is based upon our discoveryv that by exposing the surface of cuprous oxide for a limited time to the action of moist hydrogen sulfide gas, or by dipping or brushing the surface of cuprous oxide with a solution of a sulfide, such as hydrogen sulfide, sodium sulfide, etc., the several advantages hereinbefore. set forth are obtained. 7

In addition to simple sulfides, soluble poly sulfides may also be used; and also substances which react to form sulfides. Examples of such substances are sodium polysulfide, sodium thiosulfate, an alkaline solution of thiourea, etc.

While sulphur vapor produces to a limited extent the results of .the present invention, when the temperature of the gas does not exceed C.,

. the other modes of producing the cuprous sulfide film are much preferred, as the results arefmuch superior, and the procedure much simpler.

The improved results of the present invention are also obtained with the other members of the sulphur group, i. e. selenium and 'tellurium. For example, gaseous selenides, tellurides, solutions of selenides or tellurides, and solutions yielding such selenides or tellurides, give results similar to those obtained when sulphur and its compounds are used.

The method is carried out by subjecting the cuprous oxide, in one of a number of ways, to the action of an element of the sulphur group or their compounds. This may be done by subjecting the cuprous oxide to the action of a gas or vapor of a compound of the element, or to a solution of an appropriate compound of an element of the sulphur group. According to our experience the best results are obtained when dilute solutions are used. One percent solutions have been found to be effective. Generally it is photo-activity over a relatively long period of preferable to use a solution of a soluble sulfide time and do not suffer appreciable deterioration such as sodium sulfide. When the cuprous oxide due to ordinary handling, use, ageing, or to is treated in or with a solution it is afterwards harmful interaction with the atmospheric conrinsed in water and dried. 5 stituents.

When subjected to the action of a compound The increased stability and freedom from deof sulphur, there is formed on the surface of teri oration of elements according to our inventhe cuprous oxide a very thin and adherent tion-may be explainedb'y the adherent film of grayish film of cuprous sulfide CuzS); and copper sulfide (or tellurideor selenide) produced similar films are formed when compounds of by our method. These substances (copper sulthe other elements of the sulphur group are fide, copper selenide, copper telluride) are relaused. 7 I I tively stable, especially in city atmospheres, be-

After the element has been sensitized as preing not readily susceptible to oxidation by the viously described, it is adapted or modified for oxygen of the atmosphere, or to interaction with use in a photo-sensitive apparatus, or in a cur: 1 5 carbon dioxide of the air. In previous sensitizrent rectifying apparatus, in any suitable or ingprocesses, the photo-sensitive surface was well-known manner. v I thoughtto comprise freshly reduced copper (see Referring to Fig. 1, numeral l0 designates a Muller and Teeters loc. cit. p. 471; also B. Lange sheet of copper, having a layer H of cuprous -Photoelements" I. (Barth, Leipzig) p. 34 (1936);

oxide thereon. The cuprous oxide may be formed freshly reduced copper is known to be chemion the copper ill by thermal oxidation, or by cally active and would readily react with the electrodeposition, according to known methods. oxygen or carbon dioxide of the atmosphere, Numeral l4 designates the thin film of cuprous with a consequent decreasein photo-activity. sulfide which is formed when the cuprous oxide Another advantage offered by the present inlayer I2 is subjected to the action of a comvention lies in the fact that the adherent, active, pound of anelement of the sulphur group, acfilm of copper sulfide (or copper-selenide or cording to the method herein described. When telluride) improves the electrical conductivity selenium or tellurium compounds are used, the between the cuprousoxide layer and the front film I4 is copper selenide or copper telluride. On electrode connecting the photocell to an exterthe face of the element in contact with the na] circuit, and also provides a good and stable copper sulfide film there is a front electrode I6, electrical contact between the cuprous oxide which is here shown as a pressed-on metallic layer and thefront electrode, thereby increas grid. Alternatively, a front. electrode may be ing the efiiciency and stabilityof the photocellzj applied byspraying, evaporating, or sputtering There are the same advantages when the ele-' on to the surface It a translucent metal film. ment is used in a rectifier. The rectifying ap- Referring to Fig. 2' the parts l0, l2 and I have paratus is more efficient, and has greater stability the same structure and composition as they have than heretofore, when equipped with anelement' in the element of Fig. 1. A front electrode is according to the present invention. In rectifiers provided by applying a sheet of metal I8, adit is important, in order to-obtain good oper'at-' vantageously lead or tin, to the film H. 40 ing efiiciency and to minimize the'amount of Conducting wires are attached to the copper heat developed in operation, thatgood electrical sheet I0 (back electrode) and to the front elecconductivity and good electrical contact be maintrode or grid |6,Fig. 1. In Fig. 2 the electrical tained between the cuprous oxidelay'er of theconnections are made to copper sheet l0 (back rectifier and the front electrode. These goodelectrode) and to the lead or tin sheet l8 (front properties are obtained according to our inven-' electrode). tion by the cuprous sulfide film between the The increase of photo-electric sensitivity ofcuprous oxide and the front" electrode.

elements produced according to the present in- The improvement in efficiency of photo-sens! vention is shown by the following comparison. At tive cells and of rectifiers, resulting from our inan illumination intensity of 2000 lux, with8square vention persists over long periods of time, thus centimeters of surface exposed, an untreatproviding a stability of operation. in prolongeded cuprous oxide cell generated a.photo-cnrrent use which has been hitherto unobtainable from' of 3.0 microamperes. The element is then dipped photocells or rectifiers of thecuprous oxide type.

in a 1% solution of sodium sulphide for 20 sec- Photo-sensitive cells provided "with I elements onds, rinsed and air dried. This results in the made according to the present invention have formation on the cuprous oxide surface of a been under test for three-month periods .with'a very thin, adherent, grayish film of cuprous suldecrease of efiiciency of less than 10%.

Dhide (CuzS), h ving a thickness on the order This application is a continuation of our apof 400 Angstrom units, or 0.000004 centimeter. plication Serial No. 352,134, filed August 10, 1940; The element, after the aforesaid treatment, un- What is claimed i 4 i r der the same conditions of illumination and 1. An improved element for photocells and recmeasurement as before, generated a photo-curtifiers, having light-sensitive and asymmetrical rent of 300 microamperes, an increase of one conducting electrical properties,'comprising cup hundred fold, or ten-thousand percent. This rous oxide and a thin film having'athicknesson we explain in part by the fact that, while the 5 the order of 400 Angstrom units consisting of a specific resistance of CuzS '(cuprous sulphide) is compound of copper and an element of the sul greater than that of CmO the nature of the phur group on the cuprous oxide.

CuzS surface is such that the conductivity across 2. An improved element for photocells and the meeting-faces of the CuzS and the front elecrectifiers, having light-sensitive and 'asymmettrode l6 (air-gap) is greatly improved, and also 7 rical conducting electrical properties, comprising because of the presence of a greatly increased cuprous oxide and a thin film having'a thickness number of photo-active centers. Y on the order of 400 Angstrom units consistingof An advantage offered by the sensitization cuprous sulfide on the cuprous oxide.

process of the present invention is that photo- 3. An improved element for photocells and rec-' cells so sensitized have an increased stability and tifiers, having light-sensitive and asymmetrical conducting electrical properties, comprising cuprous oxide and a thin film having a thickness on the order of 400 Angstrom units consisting of copper selenide on the cuprousv oxide.

4. An improved element for photocells and rectifiers, having light-sensitive and asymmetrical conducting electrical properties, comprising cuprous oxide and a thin film having a thickness on the order of 400 Angstrom units consisting of copper telluride on the cuprous oxide.

5. A method or making improved elements for photocells and rectifiers having light-sensitive and asymmetrical conducting electrical properties, comprising exposing the cuprous oxide portion of such an element to the action of an 7 element of the sulphur group or a compound thereof only long enough to form a film having a thickness on the order of 400 Angstrom units.

6. A method of making improved elements for photocells and rectifiers having light-sensitive and asymmetrical conducting electrical properties, comprising exposing the cuprous oxide portion of such anelement to the action of sulphur or a compound thereof only long enough to form a film having a thickness on the order 0! 400 Angstrom units.

7. A method of making improved elements for photocells and rectifiers having light-sensitive and. asymmetrical conducting electrical properties, comprising exposing the cuprous oxide portion of such an element to the action of selenium or a compound thereof only long enough to form a film having a thickness on the order oi 400 Angstrom units.

8. A method of making improved elements for photocells and rectifiers having light-sensitive and asymmetrical conducting electrical properties, comprising exposing the cuprous oxide portion of such an element to the action of tellurium or a compound thereof only long enough to form a film having a thickness on the order of 400 Angstrom units.

9. A method according to claim 5, wherein the element or its compound is in the form or a solution to which the cuprous oxide is exposed.

10. A method according to claim 5, wherein the element or its compound is in the form of a gas or vapor to which the cuprous oxide is exposed. 11. A method according to claim 5, wherein the element or its compound is in the form of a dilute solution of a sulfide or of a compound.

which reacts to form a sulfide, to which the cuprous oxide is exposed. 

